We propose to investigate the interaction between macromolecular polyelectrolytes as a function of their separation. This is the type of problem that has been studied in the classical theory of colloid stability for many years, but here we propose several major modifications of the classical theory that are particularly appropriate for biologically-occuring polyelectrolytes rather than systems such as metallic colloids, etc. One of these modifications is to avoid the assumption that the surfaces of the particles have fixed charge or a fixed potential. Instead we propose to place ionizable groups such as -COOH and -NH2 on or near the surfaces of the polyelectrolytes and then to allow these groups to ionize or not ionize in response to the local hydrogen ion activity; this in turn is a function of bulk pH, ionic strength, and the proximity of other polyelectrolytes. We plan to calculate the electrostatic potential and hence the electrostatic free energy for several models by a variety of methods, ranging from the Poisson-Boltzmann equation to recent statistical mechanical theories of electrolyte solutions. This electrostatic free energy is then added to the inherent long-range van der Waals attraction between the charged macromolecules to give the total interparticle potential energy function as a function of pH and ionic strength. The van der Waals attraction is calculated by a method intermediate to the rigorous modern theory of macroscopic van der Waals forces developed by Lifshitz et al. and the classic pair-wise summation approach of colloid theory due to Hamaker.